﻿// Spun AJAX Framework
// Copyright (C) 2008 Blake Hegerle
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Spun.Naming.Paths;
using Spun.Naming;
using Spun.Models;

namespace Spun.Bindings.Observation
{
    internal class BoundModelObserverNode : ObserverNode
    {
        internal BoundModelObserverNode(ObserverNode Next, Path Path, BindingContext BindingContext)
            : base(Path, BindingContext)
        {
            this.Next = Next;
        }

        internal override void Update()
        {
            UnregisterForModelUpdateEvent();

            CurrentValue = GetCurrentValue();

            if (CurrentValue == null)
            {
                Next.Invalidate();
            }
            else
            {
                CurrentValue.MemberChangedEvent += MemberOnObservedModelDidChange;
                Next.Update();
            }
        }

        internal override void Invalidate()
        {
            UnregisterForModelUpdateEvent();

            CurrentValue = null;

            Next.Invalidate();
        }

        private void UnregisterForModelUpdateEvent()
        {
            if (CurrentValue != null)
                CurrentValue.MemberChangedEvent -= MemberOnObservedModelDidChange;
        }

        private ModelBase GetCurrentValue()
        {
            try
            {
                object Value = Resolver.Resolve(Path);

                if (Value == null)
                    return null;

                ModelBase Model = Value as ModelBase;

                if (Model == null)
                    throw new ObjectInModelChainNotAModelBase(Path, Value);

                return Model;
            }
            catch (CouldNotResolvePath)
            {
                return null;
            }
        }

        private void MemberOnObservedModelDidChange(ModelBase Model, string MemberName, object OldValue, object NewValue)
        {
            using (BindingContext.LockingContext.WriteLock)
            {
                if (RefersToNext(MemberName))
                {
                    if (NewValue != null)
                    {
                        Next.Update();
                    }
                    else
                    {
                        if (OldValue != null)
                            Next.Invalidate();
                    }
                }
            }
        }

        private bool RefersToNext(string MemberName)
        {
            return new PropertyPathNode(MemberName).Equals(Next.PathNode) ||
                MemberName.Equals(Next.PathNode.ToString());
        }

        private ModelBase CurrentValue;
        private readonly ObserverNode Next;
    }
}
